i do not know if this is your problem or not, but a friend and i both where using specktrum,when i started having some of the same problems as you describe. at first the tech help said it was the motor, got new motor, still had problem, then it was esc, got new esc, still had problem, then sent rx's in and returned, still had problem, the last time i was the talking to some higher tech. the problem according to him was the group of things, stock motor, Q2 esc, jr9000s servo, high traction, causing a voltage drop. the fix is a 5.99 capacitor that spektrum sells. never had a problem again. that was in my stock bk2, stock mf2
this may help??
i still race.